One-package heat-curable urethane polymer casting composition

ABSTRACT

A one-package heat-curable urethane polymer casting composition which comprises three components is disclosed. The first component is a urethane prepolymer in which the isocyanate terminals have been blocked with a high molecular weight, solid, non-volatile, substituted phenol. The second component is a curative diamine in curative amounts. The third component is an organic acidic material in stabilizing amounts. The resultant composition of these components is stable at ambient temperature conditions. On the application of heat, however, this composition forms a void-free polyurethane which maintains its desirable urethane properties. Said composition is designed to be cast into thick sections, as opposed to thin films or coatings.

United States Patent [191 Mazzeo et al.

[ lMarch 20, 1973' ONE-PACKAGE HEAT-CURABLE URETHANE POLYMER CASTINGCOMPOSITION [75] Inventors: TVIichael P. Mazzeo, l-lightstown, N.J.;Riad H. Gobran, Levittown; Anthony F. Santaniello, Newtown; Marina N.Gillis, Morrisville, all

[21] App]. No.: 210,195

Related U.S. Application Data [63] Continuation-impart of Ser. No.77,354, Oct. 1,

i970, abandoned.

52 us. Cl...260/45.7 R, 260/775 ss, 260/77.5 TB 511 int. Cl ..C08g51/53, C08g 22/32 58 Field of Search..260/75 NH, 77.5 TB, 77.5 AM,

260/775 ss, 45.7 R

3,179,625 4/1965 Ehrhart ..260/77.5 SS X 3,252,848 5/1966 Borsellino..260/77.5 AM X 3,499,852 3/1970 Schroeder et a] ..260/77.5 TB X OTHERPUBLICATIONS Dictionary of Organic Chemical Cpds., Vol. 3, Oxford (NewYork) 1965, page 1660.

Primary ExaminerDonald E. Czaja Assistant Examiner-H. S. CockeramAttorney-Thomas W. Brennan [5 7] ABSTRACT A one-package heat-curableurethane polymer casting composition which comprises three components isdisclosed. The first component is a urethane prepolymer in which theisocyanate terminals have been blocked with a high molecular weight,solid, non-volatile, substituted phenol. The second component is acurative diamine in curative amounts. The third component is an organicacidic material in stabilizing amounts. The resultant composition ofthese components is stable at ambient'temperature conditions. On theapplication of heat, however, this composition forms a void-freepolyurethane which maintains its desirable urethane properties. Saidcomposition is designed to be cast into thick sections, as opposed tothin films or coatings.

20 Claims, No Drawings ONE-PACKAGE I'IEAT-CURABLE URETHANE POLYMERCASTING COMPOSITION CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of application Ser. No. 77,354,filed Oct. 1, 1970 and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to one-package high molecular weight urethane casting polymers,a process for producing the same, and a casting produced therefrom.

More particularly, this invention relates to the preparation of aone-package urethane polymer composition which may be cast to yield asolid, void-free polyurethane section. More particularly, this inventionrelates to the preparation of a solid polyurethane elastomer which isproduced by the heat-curing of a blocked urethane prepolymer which is ina single package with a curative and stabilizing organic acid.

Polyurethane elastomers are extremely useful because of theircharacteristic properties which include high strength, abrasionresistance, and hardness. Thus they are widely used in diverseapplications such as for example, heel lifts and small industrialwheels.

2. Description of the Prior Art It is conventional in the art to formpolyurethane elastomers by first forming a basic intermediate which is alow-molecular-weight polymer with hydroxyl endgroups. The basicintermediate isthen reacted with an aromatic diisocyanate to give anisocyanate-terminated polyol which is termed the prepolymer. Thefinished polyurethane is then prepared by admixing the prepolymer with acurative such as a glycol, a diamine, a diacid, or an amino alcohol.

However, the prepolymer and the curative react very rapidly, having apot life of, typically, only minutes before the mixture sets up. Also,the amounts of these two conventional reactants must be preciselycontrolled to provide the critical stoichiometry which will lead to auseful cured rubber. Furthermore, the prepolymer is sensitive toatmospheric moisture and must be handled with care to prevent prematurereaction of the isocyanate (NCO) terminals.

The present state of the art for polyurethane casting polymers is toprovide a two-package system wherein one package contains the prepolymerwith the active NCO terminal groups and the other package contains thecurative as is disclosed in prior U.S. Pats. such as Nos. 2,801,990 and3,084,182. This system has several disadvantages. Four of the moreundesirable features are that (l) the ingredients of the two packagesmust be mixed shortly before use because of the short pot life mentionedpreviously, (2) the ingredients must be measured exactly immediatelyprior to casting the polymer which requires expensive and specialmetering and mixing equipment, (3) the cumbersomeness of the two packagesystem, and (4) the toxic hazards due to the dust and fume exposure ofthe metering operation.

Blocked isocyanate prepolymers are isocyanate derivatives that areessentially unreactive at ordinary or ambient temperatures, therebyallowing them to be mixed with curatives (active hydrogen containingcompounds), but which react like isocyanates when raised to a hightemperature. These blocked prepolymers have been used in a singlepackage in the past to make thin films or coatings only, as shown inU.S. Pat. Nos. 2,984,645; 3,084,182; 3,252,848 and 3,499,852. However,these compounds have not produced satisfactory thick castings due to thereduced urethane properties and the holes or voids in the casting causedby the volatilization of the blocking agent.

These thermolabile blocked isocyanates are the reaction products ofisocyanate-terminated prepolymers with blocking agents which areadduct-forming compounds that are simple mono-reactive materialscontaining a reactive hydrogen atom. The reaction products arefrequently referred to as isocyanate adducts. These adducts areoccasionally referred to as isocyanate generators, -the implicationbeing that they actually dissociate on heating to thereby form freeisocyanate groups which then react in the usual way. However, some ofthose skilled in the art believe that these masked isocyanates producesome, if not all, of their curing effects by an interchange mechanismanalogous to ester-interchange.

The temperature at which such adducts afford isocyanate-type curesdepends upon the nature of both the isocyanate prepolymer and theblocking agent, as well as that of the curative. Blocking agents thathave been previously employed in the production of urethane filmsinclude imines, oximes, amines, alcohols, and phenol. For a givenisocyanate, phenol adducts are among the most labile and are veryreactive at about C.

Blocked isocyanates of the above types have been tried in a variety ofsolid polyurethane applications, as opposed to foamed polyurethane.Their use in practice has been limited, however, due to a number ofdeleterious problems and side effects. These include (1) the release ofobjectionable odors from a phenol blocking agent; (2) the'difficulty inobtaining a satisfactory cure at temperatures below about 150C; (3) theholes or voids in the finished casting caused by the escaping blockingagent; (4) the poor physical properties due to the previously mentionedholes; and (5) the incompati-' bility of the blocking agent with thecured polyurethane polymer causing the blocking agent to bleed out" ofthe molded product and to form a powder or oily film on the surface ofthe product. These problems are unimportant in thin-film systems orsurface coatings or adhesives, but in the preparation of thick castingsthey are extremely critical.

Most important to this invention, previous attempts at achieving thecombination in a single package of the reactants necessary for arapid-curing polyurethane have been largely unsuccessful. In particular,the resulting cured polymer product did not possess the propertiestypical of a conventionally prepared polyurethane, especially when usedto produce a solid polyurethane section which has a thickness greaterthan 1 inch. Specifically, the resulting polymer was not bothelastomeric and strong.

Accordingly, it is an object of this invention to provide an improvedprocess for unblocking and curing a blocked isocyanate prepolymer in asingle package with a curative and a stabilizer.

Another object is to provide an improved onepackage heat-curableurethane polymer casting composition.

Another object is to provide cured polyurethane elastomeric sectionswhich are restricted in thickness only by the characteristics of themold.

It is a particular'object of this invention to prepare a one-packageurethane casting composition which will produce solid, void-freecastings from about one-sixteenth inch thick, to a maximum thicknesslimited only by the capacity of the mold.

SUMMARY OF THE INVENTION In accordance with the above and other objectsof this invention, a pourable liquid resin composition comprisingvarious components present in a single package in a non-reactive stateat conditions of ambient temperature has been provided. Saidsinglepackage composition, upon brief application of heat atconventional curing temperatures, can be readily activated to provide asolid, void-free polyurethane 'elastomeric rubber having the propertiesof a conventionally formed polyurethane, even when cast into a thicksection, of, for example, 2 inches. Specifically,

compound. This blocked-prepolymer exhibits relativetetrahydronaphthlenel ,5-diisocyanate. may be difunctional ormultifunctional.

This NCO-terminated urethane prepolymer may be formed by first reactinga polyol with an organic diisocyanate. The following is a generalexample:

The polyol More specifically, the urethane prepolymers which may beblocked to form the blocked prepolymers employed in the novelcompositions of this invention are NCO terminated materials which mayhave an ester,

ether, hydrocarbon, polysulfide, thioester, or thioether backbone. Suchurethane prepolymers and their preparation are described, for example,in Polyurethanes: Chemistry and Technology, by J. H. Saunders and K. C.'Frisch, Interscience Publishers, New York (1962), and in US. Pat. No.2,929,800. In the present invention the ether type materials arepreferred. These preferred polyethers more preferably includepolytetramethylene ether glycols. Polyether materials of this type whichmay be used include those sold under the trade name Polymeg such asPolymeg 2000, available from Quaker Oats Co. The prepolymer I which willsubsequently be blocked is formed by reactstability at-ambienttemperatures when co-mixed with the curativeamineUpo'n the applicationof conventional curing temperatures, uriblocking results and a curedrubbery void-free polyurethane is obtained even when'cas t into sectionsup to about 8 inches thick. This single package can be formed into asolid polyurethane rubber having the properties of a conventionallyformed polyurethane even when cast into a thick sec tion up to aboutinches, merely by the brief application of heat. Additionally, and quiteunexpectedly, the incorporation of an organic acid in the single-packagecomposition in small, additive, stabilizing concentrations furtherenhances the stability of the package, providing a prolonged shelf lifefor the package at ambient conditions, by preventing the displacementofthe blocking agent by the curative amine which is present in the onepackage composition.

DESCRIPTION OF THE PREFERRED EMBODIMENT Unmodified prepolymers which maybe employed in v naphthalene-l ,5-diisocyanate; and

ing the backbone raw material, preferably an ether, with one or morediisocyanate containing materials such as tolylene diisocyanate ordiphenylmethane "diisocyanate, otherwise calledmethylene-bis-(phenylene-4-)diisocyanate, in proportions such that theresulting prepolymer (precursor) has an active NCO content of about 2 to9 percent by weight. Other prepolymers may have an active NCO content ofabout 1 to 18 percent.

Other especially useful polyether polyols are of the polypropyleneglycol type which may be either diols or triol s. These are availablecommercially under the trade name of Niax polyols from- Union CarbideCorp.

Polyesters may also be employed in the preparation of urethaneprepolymers. Examples of suitable polyesters are the reaction productsof ethylene glycol, propylene glycol, and adipic acid, of butanediol andadipic acid; of butanediol and azelaic acid; or of ethylene glycol,propylene glycol, trimethylol propane and adipic acid. Another suitablegroup of polyols (of the hydrocarbon backbone type) are the poly B-Dgroup of polyols which are liquid hydroxy-terminated polybutadienehomo-and copolymers as available from Sinclair Oil Company. These areknown in the trade as poly B-D R- 15M and R-45M, which are thehomopolymers of 200 poise and 50 poise viscosity, respectively.Copolymers which are liquid and are based on the hydroxy terminatedpolybutadiene resins and also available from the same source are thepoly B-D CS-lS butadienestyrene copolymers of about percent weightpercent butadiene and 25 percent weight percent styrene in the resins,and having a viscosity of about 25 poises, and Poly B-D CN-l5butadieneacrylonitrile copolymers of about 85 percent by weight ofbutadiene and 15 percent by weight of acrylonitrile in the polymer andhaving a' viscosity of about 500 poise.

A further polyol and prepolymer (of the polysulfide backbone type)useful for the present purpose is disclosed in U.S. Pat. No. 3,386,963by Santaniello and incorporated herein by reference. Briefly, thispolyurethane prepolymer is derived from a hydroxy-groupcontainingpolysulfide polymer and a diisocyanate reacted such that the ratio ofisocyanate groups to hydroxyl groups is between 1 and 4.

Polyols of the thioether backbone type may also be employed inaccordance with the invention. Hydroxy- NCO groups sufficiently so thatthe NCO terminated v prepolymer when blocked can be mixed with the'amine curative without a reaction taking place until heat is applied forunblocking. No blocking agents were found that by themselves wouldaccomplish this requirement. It was discovered that the more basic theamine curative the harder it was to prevent it from reacting with theblocked urethane prepolymer. However, the nonvolatile, high molecularweight, substituted phenolic compounds which are employed in thisinvention were the most successful in preventing the reaction. Thesubstituted phenolic compounds used inthis invention block the NCOgroups, even without a stabilizer, to

such an extent that the reaction takes place very slowly.

Due to the slowness of the reaction the shelf-life of the one packagesystem is greatly enhanced.

Another equally important property which :the blocking agent mustpossess in the casting polymer system is that of being non-volatile.This property is im-' portant when the blocking-agent is released, byheating the casting polymer during the curing operation, so that theblocking agent does not volatilize into the .surrounding polyurethanemolded product. vIf volatilization were to occur, the blocking agentwould cause bubbles to form in the moldedproduct. The specificsubstituted phenolic compounds suitable for use-inthis invention do notvolatilize within the polyurethane casting polymer during the castingprocess. Therefore, no bubbles or voids are formed inthe finishedproduct.

While some of the phenolic compounds do volatilize generally, the termnon-volatile whenreferring to these compounds-means'they donotvolatilize under the particularconditions of use in this'invention;i.e., these high molecular weight phenolic compounds when released fromthe prepolymer inside the urethanecasting polymer during thecuring stagedo not cause bubbles to form inside the molded polymer, whereas, the lowmolecular weight phenols will volatilize under these conditions andcause bubbles or voids to form inside the molded-polymer.

Another critical property which the blocking agent must possess is theproperty of being compatible with the polyurethane casting polymer afterthe blocking agent has been released within the polyurethane castingpolymer itself. This property is necessary since a large portion of theblocking agent remains in the polymer after curing has completelyoccurred. Were the blocking agent to be incompatible with the curedpolyurethane polymer, then the blocking agent would slowly bleed out ofthe molded product giving off an undesirable odor and forming a powderor oily film on the surface of the product.

These properties are critical only when thick castings of polyurethaneare made. When a thin film is desired, almost any blocking agent will besatisfactory as it will evaporate from the thin film during the curingprocess thereby making bleed out not a problem later on.

Therefore, the blocking agents which are suitable for this invention arethe non-volatile, high molecular weight, substituted phenolic compounds.Particularly suitable are the bisphenols, diand tri-hydroxy substitutedbenzenes, and substituted phenols where the substituent is on thearomatic nucleus, all of which are compounds with molecular weight aboveabout 110. The preferred blocking agents are the monofunctional highmolecular weight substituted phenols in which the molecular weight isabove 150. 'Most preferred is paraphenyl-phenol.

in forming the blocked prepolymers, the prepolymer and blocking agentare reacted in the ratio of approximately one,or slightly less,equivalent or mole of active NCO units to .1 mole ofsubstituted-phenolic blocking agent. :lf too much prepolymer isemployed, an unstable system which tends to gel will be obtained. Toomuch blocking agent is also undesirable. 'It is preferable to react theprepolymer and the blocking agent in the presence of a catalyst.

- cording tothe following generalfforrnulat wherein R stands :for anysubstituent(-s) on :the phenol which .will result in the high molecularweight, nonvolatilesubstituted phenolwhichis suitablefor use as'theblocking agent of thisinvention.

package polyurethane'casting polymer systems-In this amine.cure,ithe NCOgroups when unblocked undergo ing reaction would take place without theacid.

chloroaniline), 3,3-dichloro-4,4'-diaminobiphenyl,chloro-m-phenylenediamine, and 3,3-4,4'- tetraaminobiphenyl.

These curatives are present in general curative amounts which is fromabout 1 to 12 percent of the composition. Preferably 1-8 percent of thecomposition, and most preferably 2-5 percent of the total weight of thecomposition is the diamine curative.

The general reaction for the cure of an active iso-' cyanate-terminatedprepolymer with a diamine such as p-phenylenediamine is as follows:

Acidic materials preferred for use as stabilization aids are organicacids such as acetic, adipic, acrylic and cinnamic acids. These acidsare present in stabilizing amounts; i.e. about 0.3-3 percent by weightof the composition, preferably, 0.5-2 percent, and .most preferably 0.61.5 percent.

If desired, the one package compositions of this invention may furtherhave included therein in catalytic quantities a cure catalyst (cureaccelerator) such as lead octoate.

The following non-limiting illustrative examples 'will serve to moreclearly illustrate the preferredoperation of this invention. Unlessotherwise stated, all parts, proportions or percentages are by weight.

EXAMPLE I A prepolymer is prepared as follows.

3,527.5 grams of poly (tetramethylene ether) glycol, molecular weight1990, are charged into a 5-liter resin pot fitted with a cold watercondenser stirrer, and heating mantle, and heated under a N atmosphereto 100C. Vacuum is applied for one-half hour at 100C. N flush is thenresumed, and the dried polyether is cooled to 65C. 582.2 grams oftolylene diisocyanate HOH The general reaction for the cure of a blockedurethane prepolymer with a diamine is the same as above except for theadditional release of two molecules of the blocking agent per moleculeof the diamine. I

if the blocked prepolymer of this composition were put in a one-packagesystem'with just the curative there would be a slow reaction betweenthem which would limit the shelf-life of the composition to only a fewdays. However, the addition of a stabilizing amount of an organic acidis added to the one-package system to prevent the displacement of thesubstituted phenolic blocking agent by the amine curative which ispresent. The organic acid is added to give stability to the blockedprepolymer-curative composition. The follow- This reaction is affectedby the basicity of the amine; i.e., if the amine is a strong base andrich in electrons, then the reaction is very difficult to completelyprevent even with the stabilizing acid present.

Therefore, this invention uses less basic amines such as the aromaticdiamines above, together with an organic acid in making a stableone-package polyurethane casting polymer composition.

are then added. The reaction mixture is then heated to 90C. where it ismaintained for 5 hours. The resulting prepolymer is discharged into acan and sealed under N It is then stored at 65C overnight.

The prepolymer is blocked and curative (curing agent) agent) and acidare added'thereto as follows.

500 grams of the previously prepared warm prepolymer arecharged into a2-liter resin pot. 67.5 grams of para-phenylphenol are then weighed intothe prepolymer. The reactor is assembled, and heat (from a heatingmantle), agitation (with a double-paddled agitator) and N, are applied.At C 0.25 grams of triethylenediamine are added; The reaction mixture isthen heated to C and allowed to react for 1.5 hours. It is then cooledto 65C and 18.6 grams of meta-phem ylenediamine are then added. Themixture is blended at 65C for 5 minutes, and finally 5.7 grams ofacrylic acid are added and blended in. The product is discharged into acan and sealed under N [In the blocking reac-. tions of polyester-based(rather than polyether-based) prepolymers, the blocking reaction is moretypically run for 5 hours at 90C.]

The resulting preferred single-package composition of this inventioncontains the following three components.

l. The prepolymer of poly(tetramethylene ether) glycol, molecular weight2,000, and tolylene diisocyanate, reacted in a ratio of 1.9 equivalentsNCO/equivalent OH, having isocyanate terminals blocked withparaphenylphenol. e

2. Meta-phenylene diamine 1.05 equivalents of dormant NCO/equivalent ofNH 3. Acrylic acid (1.0 grams/ grams of blocked prepolymer).

This package has an initial viscosity at 120Fof 630 poises and astability at 120F of 12 days or longer.

The above single package is compression-molded at 150C for one-half hourand post-cured at 90C for 16 hours to produce a molded productone-eighth inch having the following physical properties:

Ultimate tensile 4200 psi Ultimate elongation 870% Duro, Shore A 76 100%Modulus 460 psi 300% Modulus 700 psi 500% Modulus 1200 psi Tear, Die C390 pli Compression set 42.3%

(22 hours, 150F plied) Additional compression moldings were made whichwere one-half inch, 1 inch, and 1 2% inches thick under similarconditions.

EXAMPLE 2 A single package is prepared as in Example 1 but from ablocked prepolymer prepared from an NCO terminated prepolymer based onan ethylene-propylene adipate polyester and tolylene diisocyanate(Thiokol Solithane 291, a registered trademark) and acetic acid (presentat a 0.9 percent level, based on the weight of blocked prepolymer). Thesame proportion in the package of meta-phenylene diamine is employed asin Example 1. Para-phenol phenol was used .as the blocking agent as inExample 1.

The resulting package has an initial viscosity at 120F of 920 poises anda stability at ambient temperature of 72 days or longer.

A )6 inch thick molded product prepared using the molding conditions ofExample 1 .is found to have the following physical properties:

Ultimate tensile 1340 psi Ultimate elongation 810% Duro, Shore A 74 100%Modulus 440 psi 300% Modulus 550 psi 500% Modulus. '860 psi Tear, Die C205,pli Compression set 517% (22 hours at 150F., plied) EXAMPLE 3 Asingle package is prepared as'in Example2 butemploying acrylic acid at a1.0 percent level, based on weight of blocked prepolymer.

The resulting package has an initial viscosity at 120F of 900poises-anda stability at 120F of 41 days or longer.

A molded'productpreparedusing the-molding conditions of Example '1 isfound to have the following physical properties when using astandard /fiinchthick sample:

Ultimate tensile 1420 psi Ultimate elongation 785% Duro, Shore A 74 100%Modulus 400 psi 300% Modulus 520 psi 500% Modulus 810 psi Tear, Die C255 pli Compression set, 52.3%

(22 hours at 158F., plied) EXAMPLE 4 A single package is prepared as inExample 2 but employing para-benzyloxyphenol as the blocking agent.

The resulting package has an initial viscosity at 120F of about 920poises and a stability at 120F of 19-21 days.

A molded product prepared by gel-molding at 150C for 50 minutes followedby 16 hours of post-curing at C is found to have the following physicalproperties:

Ultimate tensile 445 psi Ultimate elongation 520% Duro, Shore A 72Modulus 340 psi 300% Modulus 375 psi 500% Modulus 445 psi Tear, Die Cpli EXAMPLE 5 Asingle package is prepared as in Example 2 but employingpara-cumylphenol as the blocking agent and further having includedtherein 1 percent lead octoate (a cure catalyst).

The resulting package has an initial viscosity at (22 hours at 158F.,plied.)

EXAMPLE 6 A single package is prepared as in Example Zbutemployingcinnamic acid (presentat a 1.5 percent level, basedon the weightofblockedprepolymer).

The resulting package has an initial viscosity at 120F of 900 poises andastability at 120".F of at least 15 days.

Aimolded productprepared using the moldingconditions of Example 1isfound to havethe following physical properties:

Ultimate tensile 1590 psi Ultimate elongation 790% Duro, Shore A 75 300%Modulus 550 psi 500% Modulus 880psi Tear, Die C 260 pli Compression set35.6%

(22 hours at 158F., plied) EXAMPLES 7-10 Four-differentsinglepackages'allv containing. thefol-.

lowing components are prepared asimExample 2.

l. The prepolymer Solithane'29 l blocked with paraphenylphenol. 1

2. Adipic acid, 0.8 grams/100 grams of blocked resin.

3. An aromatic diamine curing agent (11.05 equivalents of dormantNCO/equivalent of NH A molded product is prepared from each singlepackage by molding at Cfor 30 minutes followed by 16 hours ofpost-curing at 100C.

The particular aromatic diamine employed in formulating each package andthe resulting package properties and molded product properties arelisted in Table I below.

.6 pph 9 days .0 pph EXAMPLE l3 120F of 1,260 poises and a stability at120F of 10 I days.

A molded product prepared by compression molding at 150C followed by 16hours of post-curing at 100C is found to have the following physicalproperties:

Ultimate tensile 850 psi Ultimate elongation 875% Duro, Shore A 4 64300% Modulus 265 psi 500% Modulus 325 psi EXAMPLE 1 2 Various singlepackages all containing the following components are prepared as inExample 2.

1. The prepolymer Solithane 291, having its isocyanate terminals blockedwith a phenolic compound in a ratio of 1 mole per equivalent of NCO.

2. Caytur 7 curing agent (1.05 equivalents of dormant NCO/equivalent ofN11,).

3. Adipic acid, concentration given in Table 11 (below) relative toweight of blocked resin.

The resulting single packages have a shelf stability or shelf life whichvaries with the particular phenolic compound employed as the blockingagent and with the level of adipic acid. These results are summarized inTable 11 below.

TABLE 11" EFFECT OF ACID LEVEL ON SHELF LIFE OF PACKAGE AT 120F.

Blocking Agent Bisphenol A Para-benzyl- Para-phenyl Pataphenyloxyphenolphenol Level of Adipic Acid None 3-6 l-2 days 2 days 0.2 pph lO-l3 days9-14 days 2-5 days 0.4 pph 15 days 9-14 days 5-7 days 5 A single packageis prepared as in Example 1 but 1W 7 TABLEI M Q 7 Choice of aromaticdiamine curing agents Example 7 8 9 10 50 mol. percent Methylene eurnenediarnine; bls[ortho- 3,3'-dichloro- 50 mol. percent Methylene eh1oro-4,4-diamino metaphenylene- Physical properties of molded dianllineaniline] biphenyl diarnine product (MDA) (M0 CA) (CB U) (C aytur 7)Ultimate tensile, p.s.i 1,300 sao 1,100 1,710 Ultimate elongation,percent- 795 785 540 895 Duro Shore A. 73 58 77 63 modulus, p.s.i 350285 490 245 300% modulus, P.5d 450 355 675 300 500% modulus, p.a.i 694485 950 550 Tear, Die 0, pli 175 200 155 EXAMPLE 1 l where the polyol ofthe blocked prepolymer is poly(propylene ether)glycol and the stabilizeris acetic acid in a 0.9 percent concentration based on the weight ofblocked resin.

The resulting package has an initial viscosity at 120F., of 220 poisesand a stability at 120F of 10 days.

tions of Example 1 is found to have the following physical properties:

Ultimate tensile 540 psi Ultimate elongation 700% psi Duro, Shore A 70100% Modulus 370 psi 300% Modulus 450 psi 500% Modulus 500 psi Tear, DieC 200 pli Compression set 53.5%

(22 hours at 158F., plied) EXAMPLE 14 A single package castingcomposition is prepared as e in Example 2 with paraphenylphenol as theblocking agent.

A donut shaped molded product with outside diameter 2 inches, insidediameter five-eighths inch, and thickness one-half inch was preparedunder the follow- EXAMPLE 15 A single package casting composition isprepared in accordance with Example 2.

A donut shaped molded product was prepared with outside diameter 7 16inches, inside diameter 2 '56 inches, and thickness 1 Y4 inches.

This product was first formed by gel-molding the composition at 107C for1 hours. A second molding was then made by compression molding thecomposition at C for only 45 minutes.

A molded product prepared using the molding condi- Q We claim:

1. A one-package, stable heat-curable urethane casting polymercomposition comprising:

1. a blocked, urethane prepolymer, said prepolymer (a) having apolyester, polyether, hydrocarbon, polysulfide, or polythioetherbackbone, formed by reacting a polyol with an organic diisocyanate toform a NCO-terminated urethane prepolymer (b) being blocked with a highmolecular weight, nonvolatile, substituted phenol blocking agent, (c)having an active NCO content as present in the prepolymer prior toblocking of from about 1 percent to about 18 percent by weight, ((1)further having a ratio of NCO groups as present in the prepolymer toactive hydrogen groups as present in the blocking agent of about 1:1,and (e) having a molecular weight of about 500 to about 8,000 prior toblocking.

2. a curative amount of a multifunctional aromatic diamine curative; and

3. a stabilizing amount of an organic acid; wherein upon curing saidcomposition produces a voidfree casting.

2. A composition as in claim 1 wherein said prepolymer has a backboneselected from the group consisting of polyester and polyether backbones.

3. A composition as in claim 1 wherein said prepolymer has a polyetherbackbone.

4. A composition as in claim 1 wherein said prepolymer has a poly(tetramethylene ether) backbone.

5. A composition as in claim 1 wherein said organic diisocyanate istolylene diisocyanate.

6. A composition as in claim 1 wherein said high molecular weight,non-volatile, substituted phenol is monofunctional.

7. A composition as in claim 1 wherein said high molecular weight,non-volatile, substituted phenol is para-phenylphenol.

8. A composition as in claim 1 wherein said substituted phenol has amolecular weight above about 1 l0.

9. A composition as in claim 1 wherein said substituted phenol has amolecular weight above about 150.

10. A composition as in claim 1 wherein said multifunctional aromaticamine curative is difunctional.

11. A composition as in claim 1 wherein said organic acid is selectedfrom the group consisting of acetic acid, adipic acid, acrylic acid, andcinnamic acid.

12. A composition as in claim 1 wherein said blocked prepolymer is theadduct of para-phenylphenol and the reaction product of tolylenediisocyanate and p0ly(tetramethylene ether) glycol, said curative ismetaphenylene diamine, and said organic acid is acrylic acid.

13. A composition as in claim 1 wherein said diamine curative is l-l 2percent by weight of the composition.

14. A composition as in claim 1 wherein said diamine curative is l-8percent by weight of the composition.

15. A composition as in claim 1 wherein said diamine curative is 2-5percent by weight of the composition.

16. A composition as in claim 1 wherein said organic acid is 0.3-3percent by weight of the composition.

17. A composition as in claim 1 wherein said organic acid is 0.5-2percent by weight of the composition.

18. A composition as in claim 1 wherein said organic acid is 0.6-1.5percent by weight of the composition.

' 19. A process comprising subjecting the composition of claim 1 in amold to elevated temperature to unblock and cure the residual prepolymerin said mold, thereby forming a fully cured, molded, void-free, solidpolyurethane part having elastomeric properties.

20. A process as in claim 19 wherein said molded part has a thickness ofat least about one-sixteenth inch.

2. A composition as in claim 1 wherein said prepolymer has a backboneselected from the group consisting of polyester and polyether backbones.2. a curative amount of a multifunctional aromatic diamine curative; and3. a stabilizing amount of an organic acid; wherein upon curing saidcomposition produces a void-free casting.
 3. A composition as in claim 1wherein said prepolymer has a polyether backbone.
 4. A composition as inclaim 1 wherein said prepolymer has a poly (tetramethylene ether)backbone.
 5. A composition as in claim 1 wherein said organicdiisocyanate is tolylene diisocyanate.
 6. A composition as in claim 1wherein said high molecular weight, non-volatile, substituted phenol ismonofunctional.
 7. A composition as in claim 1 wherein said highmolecular weight, non-volatile, substituted phenol is para-phenylphenol.8. A composition as in claim 1 wherein said substituted phenol has amolecular weight above about
 110. 9. A composition as in claim 1 whereinsaid substituted phenol has a molecular weight above about
 150. 10. Acomposition as in claim 1 wherein said multifunctional aromatic aminecurative is difunctional.
 11. A composition as in claim 1 wherein saidorganic acid is selected from the group consisting of acetic acid,adipic acid, acrylic acid, and cinnamic acid.
 12. A composition as inclaim 1 wherein said blocked prepolymer is the adduct ofpara-phenylphenol and the reaction product of tolylene diisocyanate andpoly(tetramethylene ether) glycol, said curative is metaphenylenediamine, and said organic acid is acrylic acid.
 13. A composition as inclaim 1 wherein said diamine curative is 1-12 percent by weight of thecomposition.
 14. A composition as in claim 1 wherein said diaminecurative is 1-8 percent by weight of the composition.
 15. A compositionas in claim 1 wherein said diamine curative is 2-5 percent by weight ofthe composition.
 16. A composition as in claim 1 wherein said organicacid is 0.3-3 percent by weight of the composition.
 17. A composition asin claim 1 wherein said organic acid is 0.5-2 percent by weight of thecomposition.
 18. A composition as in claim 1 wherein said organic acidis 0.6-1.5 percent by weight of the composition.
 19. A processcomprising subjecting the composition of claim 1 in a mold to elevatedtemperature to unblock and cure the residual prepolymer in said mold,thereby forming a fully cured, molded, void-free, solid polyurethanepart having elastomeric properties.
 20. A process as in claim 19 whereinsaid molded part has a thickness of at least about one-sixteenth inch.